Energy & Fuels 1987,1, 89-93
89
Influence of Solvent-Free Catalytic Hydrogenation on the Thermoplastic Behavior of Coals Peter G . Stansberry,*t Rui Lin,r M.-T. Terrer,? Chun W. Lee,? Alan Davis,t and Frank Derbyshire? Fuel Science Program and Coal Research Section, College of Earth and Mineral Sciences, The Pennsylvania State University, University Park, Pennsylvania 16802 Received August 6, 1986. Revised Manuscript Received September 9, 1986
Earlier research has shown that coals hydrogenated in the absence of solvent and in the presence of a dispersed Mo catalyst become progressively more fluid. The present studies were undertaken to examine the relationships between the catalytically generated coal liquids and thermoplastic behavior. Five coals of rank varying from subbituminous to low-volatile bituminous and exhibiting little or no fluidity were hydrogenated by using an impregnated molybdenum catalyst and without vehicle for various times a t temperatures up to 400 "C. Except for the low-volatile bituminous coal, the fluid behavior of the hydrogenated coals, as measured by Gieseler plastometry and microdilatometry, was greatly improved compared to that of the untreated coals. The development of fluid behavior displayed by the hydrogenated coals is attributed to the generation of relatively small, solvent-soluble, molecular fragments. The structure of the low-volatile bituminous coal is considered to contain a large proportion of strong covalent bonds, which inhibit degradation of the coal structure. Air oxidation of a high-volatile A bituminous coal substantially reduced its fluid properties. Following catalytic hydrogenation, the hydrogenated coal became even more fluid than the original untreated coal. Microdilatometry measurements on mixtures of a high-volatile A bituminous coal with chloroform-soluble extracts, obtained from the same coal after hydrogenation, showed a progressive enhancement in swelling and lowering in softening temperature as the proportion of the extract in the mixture was increased. However, neither mixing a hydrogenated high-volatile A bituminous coal with its unhydrogenated parent coal nor mixing with the chloroform-soluble extract from a hydrogenated subbituminous coal improved the dilatation properties.
Introduction treatmenta6J2Furthermore, the lower molecular weight substances not only play an essential role in the developIt has been known for several decades that heating ment of plasticity, but also are influential in promoting certain coals a t temperatures near their softening point coal liquefaction.13J4 may result in a severalfold increase in the quantity of Although the origin of the lower molecular weight, hyextractable liquids.1-8 Further, it has been demonstrated drogen-enriched "bitumens" may be the result of the that the fluid properties of coals correlate with the yield thermal degradation of larger molecular units within the of liquids extracted after heat treatment (most often when coal into smaller, more soluble fragments,2v3y7an alternative chloroform is used as the extracting solvent) and that both suggestion is that the soluble products are already present of these characteristics pass through a maximum in coals within the ~ o a l . ' ~ Heating J~ the coal results in their being with a carbon content between 85 and 88%.5*6v9310 liberated from within the coal pore structure whereupon That the chloroform-soluble extracts are important to they become more accessible to the extracting solvent. The fluid development in coking coals has been shown by (1) latter interpretation is consistent with the view that coal blending the chloroform-soluble extracts from coking coals may be considered as comprising two phases: a relatively with noncoking coals, which can induce plasticity in the low-molecular-weight soluble phase, which is physically m i ~ t u r e , 2 (2) ~ ~removing ~ ~ J ~ the chloroform-soluble extracts held within, or weakly bonded to, an insoluble cross-linked from a coking coal, which leaves a residue no longer matrix.17 amenable to the development of plasticity,2.6(3) only small yields of chloroform-soluble extract being produced by heating coals of low or high rank (i.e., noncoking ~ 0 a l ~ ) . ~ , ~ 9 ~ and Brown Dryden and Pankhurst,2 Dryden and (1)Illingworth, S.R. Fuel 1922, 1, 213. (2) Dryden, I. G. C.; Pankhurst, K. S. Fuel 1955, 34. 363. and Watersa have shown that chloroform-soluble extracts (3) Oxley, G. R.; Pitt, G. J. Fuel 1958, 37, 19. contain a greater proportion of hydrogen than the whole (4) Ouchi, K. Fuel 1961, 40, 485. coal and that the extracts are of relatively low molecular (5) Dryden, I. G. C.; Joy, W. K. Fuel 1961, 40, 473. (6) Brown, H. R.; Waters, P. L. Fuel 1966, 45, 17. weighta4vaI t is probable that these extracts contain com(7) Lazarov, L.; Angelova, G. Fuel 1968, 47, 342. pounds that can function as hydrogen donors. (8) Yoshii, T.; Yoshimura, F. Fuel 1971,50, 122. The phenomenon of plastic behavior in coals has been (9) Sanada, Y.; Honda, H. Fuel 1966,45, 295. (10) Ouchi, K.; Tanimoto, K.; Makabe, M.; Itoh, H. Fuel 1983, 62, explained by the hypothesis that the development of 1227. plasticity is a transient, in situ, hydrogen-donor process.12 (11) Wheeler, R. V.; Woolhouse, T. G. Fuel 1932,11,44. The solvent-soluble material is thought to be responsible (12) Neavel, R. C. In Coal Science; Eds.; Larsen, J. W.; Wender, I., for solvation and hydrogen stabilization of the molecular Eds.; Academic: New York, 1983; Vol. 1. (13) Larsen, J. W.; Sams, T. L.; Rodgers, B. R. Fuel 1980, 59, 666. units in coal as they become loosened with thermal (14) Derbyshire, F. J.; Davis, A.; Lin, R.; Stansberry, P. G.; Terrer, M.-T. Fuel Process. Technol. 1986, 12, 127. (15) Vahrman, M. Nature (London) 1961, 189, 136. (16) Waters, P. L. Fuel 1962, 41, 3.
'Fuel Science Program. *Coal Research Section. 0887-0624/87/2501-0089$01.50/0
0 1987 American Chemical Society
90 Energy &Fuels, Vol. 1, No. 1, 1987
Stansberry et al.
Penn State Sample Bank no. seam county state ASTM mean-maximum reflectance of vitrinite (Romax, % ) moisture content (ar wt 70) mineral matter (dry, w t %)
PSOC-1325 L. Kittanning Somerset Pennsylvania lvb 1.63
Table I. Coal Properties PSOC-1296 PSOC-1266 L. Kittanning L. Kittanning Armstrong Mahoning Pennsylvania Ohio hvAb hvAb 0.87 0.83
1.2 13.5
20.3
carbon hydrogen oxygen nitrogen organic sulfur
90.0 5.0 2.8 1.6 0.6
vitrinite exinite inertinite
96 0
4
1.1
3.4 6.1
Elemental Composition (% dmmf) 85.7 83.2 5.5 5.0 5.8 8.6 1.5 2.1 1.4 0.5
PSOC-1022 L. Kittanning Lawrence Pennsylvania hvAb 0.80
0.40
PSOC-1414 Beulah-zap Mercer N. Dakota sub no data
3.8 17.2
17.8 11.9
25.4 10.8
82.9 5.7 7.7 1.6 0.6
73.0 4.5 20.4
71.0 6.6
1.2
0.9
0.7 0.6
87
83
2 11
2
Petrographic Composition (Mineral-Free, vol 5%) 88 81 81 2 3 13 10 6 6
Evidence relating fluidity to a two-component coal structure can be found in the work of Lynch and Webster,ls who reported that the maximum Gieseler fluidity of a New South Wales coal corresponded to a minimum in the relative intensity of the rigid component as measured by proton nuclear magnetic resonance. Sanada and Hondag measured the equilibrium swelling of coals in pyridine and calculated the mean molecular weight per crosslinked unit for a series of coals. They reported that caking coals, with about 85% carbon content had the lowest cross-link density within the series of coals studied. A decrease in the yield of extract"Jg and a significant decrease in plasticityll$mcan be effected by mild oxidation. Ignasiak et a1.21have suggested that the incorporation of reactive oxygen groups (as phenolic, acidic, or ketolic oxygen) may be responsible for the formation of cross-linkages during the heating of the coal, leading to an overall reduction in the internal mobility of the coal molecules. Conversely, hydrogenation of oxidized or high-oxygen low-rank coals can result in some development of coking behavi~r.~~-~~ Earlier research, conducted a t this university, was directed toward deriving coal structural information through low-severity catalytic hydrogenation of coal in the absence of solvent.25 The technique of dry hydrogenation, which was first used by Pelipetz and Weller,26can simplify the interpretation of the results because all of the produds are necessarily derived from coal. In the earlier studies (and in the results presented here) an impregnated molybdenum catalyst was used. It was found that, as the coals were progressively hydrogenated, their fluidity increased. Continuing research has been directed toward investigating the relationship between the catalytically generated coal liquids and fluid properties, for a series of coals ranging in rank from sub(17) Given, P. H.; Marzec, A.; Barton, W. A.; Lynch, L. J.; Gerstein, B. C. Fuel 1986, 65, 155. (18) Lynch, L. J.; Webster, D. S. Fuel 1979,58, 235. (19) Parr, S. W.; Hadley, H. F. Fuel 1925, 4 , 38. (20) Senftle, J. T.; Davis, A. Int. J. Coal Geol. 1984, 3, 375. (21) Ignasiak, B. S.; Clugston, D. M.; Montgomery, D. S. Fuel 1972, 51, 76. (22) Nandi, B. N.; Ternan, M.; Belinko, K. Fuel 1981, 60, 347. (23) Ahuja, L. D.; Sharma, J. N.; Kini, K. A.; Lahiri, A. J. Sci. Ind. Res., Sect. A 1958, 17, 27. (24) Nandi, B. N.; Ternan, M.; Parsons, B. I.; Montgomery, D. S. Abstracts of Papers, 12th Biennial Conference on Carbon, Pittsburgh, PA, July 28-August 1, 1975; p 23. (25) Stansberry,P. G.; Terrer, M.-T.; Derbyshire, F. J.; Finseth, D. H. Prepr. Pap.-Am. Chem. Soc., Diu. Fuel Chem. 1984,29(5), 67. (26) Weller, S.; Pelipetz, M. G. Znd. Eng. Chem. 1951, 43(5), 1243.
PSOC-1403 Anderson Campbell Wyoming sub
21.1
15
bituminous to low-volatile bituminous. It is the results of these studies that are presented in this paper.
Experimental Section (1) Coal Properties and Preparation. The coals studied were obtained from the Penn State Coal Sample Bank. The coals ranged in rank from subbituminous to low-volatile bituminous and all had vitrinite contents of over 80%. Some properties of the coals are shown in Table I. The coals were ground to -60 mesh (U.S. sieve size) under oxygen-free nitrogen, to minimize oxidation, and samples were then sealed in small vials. For the purposes of catalytic hydrogenation, the coals were impregnated with 1w t % of molybdenum on a dmmf basis. The imRregnation procedure was to dissolve the requisite quantity of ammonium heptamolybdate (AHM) in sufficient distilled water to give a final water to coal ratio of approximately 1.51. To ensure that the molybdenum was present as MoSz, the metal's most active form in coal hydrogenation:' the AHM was converted to ammonium tetrathiomolybdate, (NH&MoS, (which decomposes to molybdenum disulfide upon mild heatin?), by bubbling hydrogen sulfide gas through the solution for 30 min. The coal was then added to the solution, and stirred for 30 min before the excess water was removed below 100 "C under vacuum. An hvA coal exhibiting good fluidity (PSOC-1296) was chosen for the oxidation studies. Fifty grams of -40 mesh coal was fluidized with air in a quartz tube and heated at 50 "C for 4 days. (2) Hydrogenation Reactions. Hydrogenation reactions were conducted in tubing-bomb reactorsm,ma t temperatures between 250 and 400 OC for 5-60 min. Five grams of impregnated coal was charged to the bomb, which was then purged twice with nitrogen and then three times with hydrogen before finally being pressurized with hydrogen to 7 MPa. The bombs were vertically oscillated through 2.5 cm at 200 cycles/min in a preheated fluidized sandbath, which brought the reactor contents quickly to temperature. Following reaction for the desired time, the bombs were quenched to room temperature by immersion in water. In some experiments, the bombs were vented at room temperature into a glass apparatus of known volume. Gas samples were removed for analysis by gas chromatography. To determine the yields of extractable liquids and insoluble residue, the reactor contents were washed out with chloroform into a dry ceramic thimble and placed in a Soxhlet apparatus. The thimble contents were continuously extracted with chloroform (27) Anderson, R. R.; Bockrath, B. C. Fuel 1984, 63, 329. (28) Naumann, A. W.; Behan, A. S.; Thorsteinson, E. M. Proceedings
of the Climax Fourth International Conference on the Chemistry and Uses of Molybdenum; Barry, H. F.; Mitchell, P. C. H., Eds.; Climax Molybdenum Co.: Ann Arbor, MI, 1981; pp 313-318. (29) Szladow, A. J.; Given, P. H. Ind. Eng. Chem. Process Des. Deu.
1981, 20, 27. (30) Yarzab, R. 59, 81.
F.; Given, P. H.; Davis, A.; Spackman, W. Fuel 1980,
Energy & Fuels, Vol. 1, No. I, 1987 91
Thermoplastic Behavior of Coals
Table 11. Yields of Gases and Chloroform-Soluble Extract (% dmmf) from Thermally and Catalytically Treated Coalso thermal hydrogenation catalytic hydrogenation: 1% Mo; 60 min; 7 MPa Hz 60 min; 400 "C; 7 MPa Hz 350 "C 400 "C ASTM CHC13 solubles CHC13 CHC13 CHC13 coal rank parent coal solubles CO, C1-C, solubles CO, C,-C4 solubles CO, C,-C, PSOC-1325 lvb 0.6 9.3 0.6 0.1 12.9 0.2 0.4 12.8 0.1 0.7 PSOC-1296 hvAb 5.0 37.6 0.5 0.7 49.6 0.5 0.8 2.5 PSOC-1022 hvAb 13.3 0.7 0.3 54.3 1.8 1.5 PSOC-1266 hvAb 0.9 14.3 1.4 1.9 8.8 0.2 ND 59.1 0.3 0.8 PSOC-1403 sub 4.3 10.7 11.5 1.1 33.4 7.2 0.8 52.3 12.4 4.0 PSOC-1414 sub 1.3 6.2 15.9 1.1 37.0 17.2 4.1 PSOC-1296' hvAb 0.6 35.1 2.4 0.8 54.5 1.3 4.1 All yields measured directly. ND: not detected.
'Preoxidized.
under a nitrogen blanket for about 12 h. The extracts were then fitered through Whatman 42 fiiter paper, the solvent was removed in a vacuum rotary evaporator at 40-50 "C, and the resulting solid was then dried for a further 3 h in a vacuum oven at 110 "C before weighing. The insoluble residue in the ceramic thimble was dried for 12 h in a vacuum oven at 110 "C before weighing. It may be anticipated that some loss of volatiles may have occurred during the drying of the extract. The differences between the yields calculated from the weight of dried residue and gasmake and those obtained by direct measurement have shown the losses to be small for the bituminous coals and to be only a few percent for the subbituminous coals. The values reported, then, are not considered to reflect any serious error. The extract yields were reproducible to within 2%. (3) Gieseler F l u i d i t y a n d Microdilatometry. The fluid behavior of coal samples was measured with an automated Gieseler plastometer. For each determination, 5 g of -40 mesh sample were packed into a metal cylinder. The cylinder assembly was heated in a solder bath, set initially to about 200 "C, and then the temperature was raised at 3 "C/min. The standard ASTM procedure D2639-74 was used.31 The dilatation of hydrogenated coals and of mixtures of untreated coals with extracts from hydrogenated coals was determined by using a pressure microdilatometer. The equipment and procedure have been described in detail elsewhere.32 Briefly, a 75-mg sample was introduced into a silica sample holder, and a displacement probe was placed on top of the sample. A furnace was installed around the sample holder, and the entire assembly was enclosed within a pressure vessel. The system was then pressurized with 0.1 MPa of nitrogen, and heating was initiated from ambient temperature a t a rate of 20 C/min. The vertical displacement of the probe was recorded as a function of sample temperature on a X-Y plotter. Figure 1portrays the results of a typical dilatometer run and the parameters used to characterize the coal behavior. (4) FTIR a n d Proton NMR. Parent coals and coals that had been catalytically hydrogenated a t 400 "C for 1 h were analyzed by Fourier-transform infrared spectroscopy (FTIR). Following the procedure of Painter e t al.,33samples of about 1.2 mg were ground with 300 mg of KBr in a Wig-L-Bug to prepare pellets. Spectra were recorded with a Digilab Model F T S 15/B Fourier-transform infrared spectrometer. Four hundred scans (interferograms) of the sample at 2-cm-' resolution were co-added to obtain each spectrum. All spectra were normalized to a sample weight of 1mg. In order to compare and analyze spectra, methods of band deconvolution were applied by using curve-fitting techn i q u e ~ .Such ~ ~ methods made possible the resolving of the aliphatic and aromatic C-H areas, which commonly overlap in the region of 3100-2750 cm-' in the case of coals. The proton distribution of the chloroform extracts from the parent and catalytically hydrogenated coals was determined by 'H NMR and grouped into four major classes: 5.1-1.9 ppm for a-protons; 1.9-1.0 ppm for @protons; 1 . 0 . 5 ppm for y-protons; (31) Annu. Book ASTM Stand. 1985, 5.05, 361. (32) Jenkins, R. G.; Khan, M. R. Pennsylvania State University Report to EPRI, AP-2337, 1654-1654-1,April, 1982. (33) Painter, P. C.; Snyder, R. W.; Starsinic, M.; Coleman, M. M.; Kuehn, D. W.; Davis, A. Appl. Spectrosc. 1981, 35, 475.
Figure 1. Typical dilatometer run: T,'= softening temperature; T, = temperature of maximum contraction; T, = temperature of maximum expansion; T,= temperature of resolidification; V, = maximum volume contraction; V , = maximum volume expansion; V, = maximum volume of resolidification; V,,, = (V, V,) = net maximum volume expansion. 10.1-6.1 ppm for the aromatic and phenolic protons.34 The instrument used was a Bruker WP200. Deuterated chloroform or pyridine was used as a solvent, and tetramethylsilane was used as the internal reference. The aromatic proton signals were corrected when deuterated pyridine was used.
Results and Discussion The yields of gases and chloroform-soluble extract obtained after heat treatment of the coals at 400 "C for 60 min in hydrogen and after catalytic hydrogenation at 350 and 400 "C for 60 min are given in Table 11. Heating the coals in hydrogen at 400 "C caused an increase in the yield of extractables, a result consistent with the results of a number of other workers, although the increases reported here are somewhat higher. Some of the earlier studies involved heating the coals in an inert g a ~ . Other ~ , ~ work has shown that higher yields can be obtained in hydrogen, compared to nitrogen. The effects have been attributed, in part, to mineral matter catalysis.25 Catalytic reaction at 350 "C caused a significant increase in the yields of chloroform-soluble extract over those obtained from the parent coals. The greatest response was obtained with the subbituminous coal PSOC-1403, where the extract yield was significantly higher than that obtained upon noncatalytic treatment. The high yield of extract obtained for this coal at 350 "C is consistent with reported data showing that, under these reaction conditions, low-rank coals are more reactive than bituminous c0a1s.l~ Further large increases in extract yields were obtained by catalytic reaction at 400 "C, for all of the coals except the low-volatile bituminous coal PSOC-1325. It is supposed that the structure of a coal at this stage of metamorphism contains such a high proportion of strong covalent bonds that it resists degradation into lower mo(34) Analytical Methods for Coal and Coal Products; Karr, Clarence,
Ed.; Academic: New York, 1978 Val. 11,p 131.
92 Energy &Fuels, Vol. 1, No. 1, 1987
Stansberry et al.
Fluidity Change with Progressive Catalytic Hydrogenation (400%)
350 410 470 Temperature OC Coal: PSOC-1266, hvAb (a) Fluidity of Subbituminous Coals Catalytically Hydrogenated at 4OPC (Parent coals have no fluidity.)
230
290
Table 111. Dilatometric Parameters for Mixtures of Bituminous Coal (PSOC 1266) with the Chloroform-Soluble Extract of the Hydrogenated Coal w t % hydrogenated extract in mixture 0 5 10 20 softening temp, O C 435 410 395 367 temp of max contraction, "C 477 460 450 435 temp of max expansion, O C 500 487 480 485 resolidification temp, O C 500 495 % max volume" contraction 21 24 21 26 % max volume" expansion (net) 23 52 129 349 % volume expansion" on resolidification 80 349 (net)
'Measured relative
to original coal volume.
"'i 1 416
220
t
s
280
Effects of Mild Oxidation and Subsequent Catalvtic Hydrogenation on Coal Fluidity
1051
-
Parent Coal
103
I
101
j p i d i z e ; Coal following catalytic . hydrogenation
':
' E:lized,
3i2
375
z
,
\':,\', \
437
360
!
I
0
5
I
I
10
15
P 20
Figure 3. Effects of addition of chloroform-solubleextracts to whole PSOC-1266: CHC1, extracts from catalytically hydrogenated PSOC-1266; 1% Mo; 60 min; 400 OC; 7 MPa cold H,.
,\
1 250
\I Wt %Added Chloroform Extract
\ '
I
102
52
P W
- - ',7 - -;-\
.-..-..
OP 104 0
.5 E
460
340 400 TemDerature OC
500
Temperature OC Coal: PSOC-1296, hvAb (C)
and parent coals. lecular weight species, even in the presence of an active catalyst. Mild oxidative treatment of the hvA bituminous coal PSOC-1296 reduced the yield of extractable liquids from 5.0 to 0.670, and that for the thermally treated coal from 37.6 to 35.1%. However, the subsequent catalytic hydrogenation at 400 "C appeared to have more than counteracted the effects of oxidation. The oxidized and catalytically treated coal produced about 5% more extractable liquids than the unoxidized parent coal. The results of Gieseler plastometer measurements on catalytically hydrogenated and unextracted coals are shown in Figure 2. As shown in Figure 2a, with increasing reaction time a t 400 "C, the coal softening temperature was lowered and the maximum fluidity was increased, corresponding to a progressive increase in the content of extractable liquids. For times longer than 15 min, the maximum fluidity exceeded the measurable range of the instrument. Similarly, reaction for 60 min at 400 "C introduced fluid behavior to subbituminous coals. In their untreated state, these coals produced no response in the Gieseler plastometer (Figure 2b). In parallel with the lowered yields of chloroform-extracted liquids, which resulted from oxidation of the hvA
bituminous coal, the fluid properties were also suppressed (Figure 212). Subsequent catalytic hydrogenation of the oxidized coal was instrumental in increasing the fluidity above that of the original coal. It should be pointed out, however, that all of the other untreated hvA bituminous coals displayed very low fluidity; coals within this range of rank are generally expected to become fluid upon heating. It would appear that these bituminous coals may have been affected by oxidation during storage or preparation, even though precautions were used to minimize such effects. Examination of the treated coals in the microdilatometer showed that, consistent with the Gieseler measurements, the coal softening temperature had been reduced. However, upon further heating, all of the samples underwent a volume contraction without any subsequent expansion. These results are interpreted to mean that the catalytic hydrogenation had increased the coal fluidity to such an extent that, in the molten state, the viscosity was so reduced that volatile pyrolysis products could freely escape without causing the melt to swell. A number of experiments were conducted with both a bituminous (PSOC-1266) and a subbituminous coal (PSOC-1403) used to determine whether blending the hydrogenated products with untreated coals could influence swelling behavior. Mixtures of unextracted hydrogenated coals with the parent coal, in which the concentration of the former was varied up to 50 wt % did not appreciably influence the swelling behavior of either coal. However, for the bituminous coal, there was a steady reduction in softening temperature with increasing concentration of the treated coal. Blending the extract from the hydrogenated bituminous coal with the parent coal had a pronounced effect upon
Thermoplastic Behavior of Coals
coal
ASTM rank
PSOC-1.125
lvh
PSOC-1266 PSOC-1022 PSOC-1403 PSOC-1414
hvAb hvAb sub sub
Energy &Fuels, Vol. 1, No. 1, 1987 93
Table IV. FTIR and NMR Analyses of Coals and Extracts 'H NMR of CHC13 FTIR (al/ar)cH extracts, parent coal ratio, catalytically FTIR (al/ar)cH ratio, whole coal H, H, H, H, + OH treated coals 3.8 23.1 33.2 8.5 35.2 4.5 .. 23.3 7.7 20.4 44.4 11.9 11.2 21.5 11.2 9.1 17.4 48.0 13.1 21.9 13.8 12.7 26.6 37.6 13.9 2.4 16.5 21.6 11.7 58.6 27.6 8.9 57.2 30.6 3.3
swelling properties (Table I11 and Figure 3). Increasing the concentration of hydrogenated extract in the blend progressively lowered the initial softening point of the mixture and significantly increased the coal dilatation. This effect was not found with any other combination of either of the two parent coals with the extracts from the hydrogenated coals, although, in all cases, blending reduced the initial softening temperature and increased the volume contraction. The six parent coals and their unextracted catalytically hydrogenated products (reacted a t 400 "C for 1 h) were analyzed by FTIR,and the relative proportions of aliphatic to aromatic hydrogen were determined from the ratio of the corresponding peak areas. The distribution of hydrogen in the corresponding chloroform-soluble extracts was determined by proton NMR. These results are tabulated in Table IV. The ratio of the peak areas of aliphatic to aromatic hydrogen shows a decrease with increasing rank, as might be expected. A comparison of this ratio for the treated coals with that of their untreated counterparts, however, does not show any consistent effect of catalytic hydrogenation, the ratio being higher after treatment in some cases and lower in others. An examination of the proton NMR data clearly shows that the extracts produced by catalytic hydrogenation are much more aromatic than the extract from the corresponding parent coal, especially for low-rank coals. For one of the subbituminous coals (PSOC-1414) this effect is most pronounced. The y-hydrogen content decreases by almost a factor of 4, and there is an increase in a-hydrogen by a factor of about 3. This observation indicates that the catalytic or thermal processes may involve both dehydrogenation (increasing H,) and the shortening of alkyl side chains (increasing Haand decreasing HJ. An
lH NMR of CHC13 extracts, catalytically treated coal H, H,g H, H, + OH 32.4 1910 5.4 43.2 33.7 26.2 8.8 31.2 35.6 29.1 7.9 27.5 27.8 26.6
43.4 38.7
8.7 8.0
31.2 26.7
alternative explanation is that the components rendered soluble by the breakdown of the coal structure are more aromatic than the parent extract and contain much shorter aliphatic side chains.
Conclusions Dry catalytic hydrogenation of bituminous and subbituminous coals has been found to induce thermoplastic behavior, as measured by Gieseler plastometry and dilatometry, in coals that were not originally fluid either because of their rank or because they had been oxidized. The structure of coals at and above the rank of low-volatile bituminous is difficult to degrade under the experimental conditions employed, even in the presence of a catalyst. Catalytic hydrogenation of coals lower than Ivb rank results in a significant increase in the content of chloroform-soluble liquids, an improvement in fluidity, and an increase in the aromaticity of the chloroform-soluble extract as the yield of extract increases. It is assumed that the extracts from the hydrogenated coals contain a reasonable proportion of aromatic and hydroaromatic structures, which are thought to promote the plastic behavior of coals. The results presented here suggest that the phenomenon of swelling is attributable to a particular combination of the properties of the mobile liquids within coals (and added liquids such as the extract from the hydrogenated bituminous coal) together with the structural configuration of the coal macromolecular network. Acknowledgment. The authors acknowledge the support of The Pennsylvania State University's Cooperative Program in Coal Research and the Commonwealth of Pennsylvania's Ben Franklin Partnership Program for their support of this research.
